1. Field of the Invention
This invention relates to air guns as used in marine seismic exploration and in particular to a method and apparatus for improving their efficiency.
2. Discussion of the Prior Art
Air guns are commonly-used sound sources for use in marine seismic exploration for natural resources. The purpose of an air gun is to convert the potential energy of a volume of compressed air into kinetic energy in the water as an acoustic pulse. In general, an air gun consists of a chamber for containing a volume of air compressed to a pressure of several hundred atmospheres. The chamber includes one or more exaust ports that are normally closed by fast-acting valves. Upon command, the valves are momentarily opened to impulsively release jets of compressed air. Rapid expansion of the air bubble creates the desired shock wave or acoustic pulse.
Typical air guns are described in U.S. Pat. Nos. 4,114,723 and 4,180,139 which show the mechanical structure and operation of air guns. Both patents are assigned to the assignee of this invention.
I have discovered, with the aid of slow-motion photographs, that when an air gun is fired, the released air creates turbulence and vortices in the water around the gun. The conversion of the potential energy of the compressed air to kinetic or acoustic energy is therefore inherently inefficient.